1. Field of the Invention
Example embodiments relate to a method for manufacturing an electrode for an electrochromic display. Other example embodiments relate to a method for manufacturing an electrode for an electrochromic display that is capable of preventing interference (i.e. cross-talk) between adjacent pixels by which a barrier rib for separating an electrolyte is formed prior to a porous nanoelectrode.
2. Description of the Related Art
Electrochromic displays include two electrodes which face each other, and an electrochromic layer which consists of an electrochromic material and an electrolyte and is interposed between the two electrodes. Electrochromic displays are displays that use the phenomenon in which an electrochromic material shows change in color according to a potential difference applied across the two electrodes. Such electrochromic displays use the principle that when an external electrical stimulus is applied to a transparent electrode and a counter electrode between which an electrolyte is filled to create a potential difference between the electrodes, ions and electrons contained in the electrolyte migrate into an electrochromic layer to participate in a redox (oxidation/reduction) reaction, thus causing visual changes in color or shade. Electrochromic displays are currently used in information processing, including recording, display and output of information, because of their ability to control optical properties.
Conventional electrochromic displays have disadvantages of slow response speed, short lifespan, and occurrence of cross-talk between adjacent pixels caused by ion migration. Recently, an electrochromic display having a novel structure has been developed in which an electrochromic material is coated on the surface of a porous electrode composed of fine powders (U.S. Pat. Nos. 6,067,184 and 6,426,827). As a result, it is possible to realize a commercially available electrochromic display with a high response speed and long lifespan.
The ions contained in the electrolyte used for electrochromic displays are in an oxidized- or reduced-state and migrate into the space between two electrodes facing each other and thus undergo change in their state, to render electric charges to migrate into the space between the electrodes. Accordingly, the migration speed and direction of such ions greatly affect the performance of electrochromic displays. Most particularly, in a case that is designed to control the electrochromic property of a specific pixel, which is composed of the two electrodes in parallel, ions unexpectedly migrate through an electrolyte solution into the electrodes of adjacent pixels rather than those of the specific pixel, undesirably causing variation in the electrochromic property of the adjacent pixels. In an attempt to solve this problem, several techniques to control ion migration have been suggested. The most efficient method is to form a barrier rib at each pixel, which prevents ions from migrating into adjacent pixels.
A material for the barrier rib to accomplish this purpose must be physically durable and be not chemically reacted with an electrolyte solution. To realize high-resolution displays, the barrier rib having a width equivalent to the gap between adjacent pixels, needs to be formed at each pixel. For mass-production, it is preferable to use a material that is suitable for application to photolithography. Most of conventional techniques that satisfy these requirements use photoresist as the barrier rib material. In prior arts, metal oxide such as WO3 was generally used as a material for an electrode (electrochromic layer) of electrochromic displays. In this case, since the surface of the electrode is even and dense, there is no great problem in producing a barrier rib with the use of photoresist.
FIG. 1 is a process flowchart illustrating a method for manufacturing an electrode for an electrochromic display according to one conventional method. In this method, the electrode for an electrochromic display is produced by forming a wiring electrode on a substrate, forming a metal oxide electrode (electrochromic material) on the substrate and forming a barrier rib on the metal oxide electrode with the use of photoresist. However, the metal oxide electrode has several disadvantages of slow electrochromic reaction speed, high consumption powder and short lifespan, thus making it nearly impossible to realize substantially commercially available display devices.
Unlike to the metal oxide electrode, the porous fine-particle electrode recently developed has advantages of large surface area, superior electrochromism due to high-density electrochromic material, fast response speed, and long lifespan during repeated use, thus being of potential practical applications for display devices. FIG. 2 is a process flowchart illustrating a method for manufacturing an electrode for an electrochromic display using a porous nanoelectrode composed of fine particles. Referring to FIG. 2, there are two methods to produce an electrode for an electrochromic display using the porous nanoelectrode. Specifically, one is forming a barrier rib with photoresist following forming an electrode and the other is forming an electrode following forming a barrier rib with photoresist. In the former method, photoresist permeated into the porous nanoelectrode during coating makes it impossible to form normal patterns in light-exposure and development processes. This problem is inevitable even with the use of any photosensitive material, instead of photoresist.
On the other hand, in the latter method, there occurs no structural problem in the former method. However, this method is impossible to practically use, because there is no photoresist capable of exhibiting heat resistance at 450° C. to 500° C., which is a sintering temperature of the porous nanoelectrode.